Ringing arrangement for multiplex circuits



July 31, 1923.

Filed se a 24, 1919 INVENTOR.

I ATTORNEY Patented July 31, 1923.

w t t JOHN DAVIDSON, JR., OE MONTOLAIR, NEW JERSEY, ASSIGNOR TO AMERICANTELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK RINGINGARRANGEMENT FOR MULTIPLEX CIRCUITS.

. Application filed September 24, 1919. Serial No. 325,823.

T 0 all whom it may concern: a Be it known that 1, JOHN DAVIDSON, J r.,residing at Montclair, in the county of E8863- and State of New Jersey,have invented certain Improvements in Ringing Arrangements for'MultipleXCircuits, of which the following is a specification.

This invention relates to multiplex systems employing carrier currentsandmore particularly t arrangements whereby ringing or other signalingcurrents may be transmitted over the channels of such a system.

One of the features of the invention resides in the provision of asystem of relays for controlling the transmission of ringing current ineither direction at the junction point of a low frequencysignaling linewith the carrier system, said relays being so interlocked that when onerelay is actuated to control the transmission ofringing current in onedirection the transmission of ringing current in the opposite directionwill be prevented.

A further feature of the invention relates to the provision of a systemof relays for controlling the transmission of ringing current in eitherdirection at the junction point of a low frequency signaling line andthe carrier system, one of said relays being arranged to control someelement of the carrier system, such as an'amplifier, in such a mannerthat it will function as a source of re-, layed ringing current fortransmission over the carrier system, and another relay being arrangedto control the application of ringing current to the low frequencysignaling line, the relays being so interlocked that transmission ofringing current over the carrier system and over the low frequencysignaling line cannot take place simultaneously.

These features, together with other fea-' tures of the invention, whichwill more fully appear hereinafter, ma be realized in accordance withthe detailhd arrangements set forth in the following description andillustrated in the accompanaying drawing, the figure of whichillustrates a circuit diagram embodying one form of the invention.

' In the figure, ML designates a main line or circuit for thetransmission of carrier currents. Common transmitting and receivingcircuitsTL and BL are associated with the main line ML through abalanced transformer 10. 5111 order that the circuits TL and RL mayberendered conjugate so that electrical disturbances in the one will bewithout effect upon the other, the main line ML is balanced by anartificial line or network MN.

L designates a low frequency signaling line or circuit, which, in commonwith a plurality of other lines, is adapted to transmit signals over themain line ML. In the case illustrated, the line L is an ordinary lowfrequency telephone circuit. The line L is assoclated through thetransformer 11, with an outgoing carrier transmission channel TL and anincoming carrier receiving channel RL These two channels are renderedsubstantially conjugate by providing an artificial line or network N forbalancing the line L,. The channels TL and RL are associated with thecommon circuits TL and RL through filters TF, and RF respectively.Similar channels corresponding to be associated with the circuits TL andRL through filters TF, and Rlflrespectively. These filters arepreferably of the broad band type disclosed in the U. S. patents of\George A. Campbell, Nos. 1,227,113 and 3 1,227,114, dated May 22, 1917.Said filters are designed in accordance with the principles of theCampbell patents above referred to, in such a manner that they willtransmit bands of frequencies in the neighborhood of the carrierfrequency assigned to the channel, the band's being of suflicient widthto accommodate the frequency yariation due to the modulation of thebasic carrier frequency by the signaling frequencies. The bandstransmitted by the filters TF, and RF may in practice be the same. Thebands transmitted by other filters, such as TF, and RF should besufiicientl remote from the bands transmitted by t e filters TF, and RFto allow for frequency separation between the channels.

The transmitting channel TL includes a modulator MD a band filter TF andan amplifier TA,. The modulator M may be of any well-known type, but isillustrated as a duplex vacuum tube modulator of the type illustratedand described in the U. S. application of John R. Carson, Serial No. 157,413, filed -March 26, 1917. The modulator is supplied with carriercurrents of the freother low frequency signaling circuits mayquencyassigned to the channel, over a air modulator unless the circuitis unbalanced, due to the application of signaling current thereto. I

The filter TF, is of the general type disclosed in the Campbell patentabove mentioned and is designed to suppress voice frequencies and freelypass carrier frequencies. The amplifier TA, may be of any wellknowncharacter, but is preferably a duplex vacuum tube amplifier, which, asis well known, provides a minimum degree of distortion at highfrequencies and hence is well adapted for the amplification of carriercurrents.

The receiving or incoming channel BL, includes a detector or demodulatorD,. This demodulator may be of any well-known type, but is preferably aduplex vacuum tube modulator of the general character illustrated anddescribed in the U. S. application of John R. Carson, Serial No.157,414, filed March 26. 1917. The duplex demodulator described in thesaid Carson application operates upon the so-called homodyne method ofreceiving and consequently is supplied from the circuit 13 withoscillations of the carrier frequency assigned to the channel.

The oscillations supplied from the circuit 13 react in a well-knownmanner With the received modulated currents, to detect the low frequencysignaling currents.

The channel 'RL, also includes an amplifier RA,. This amplifier ispreferably a vacuum tube amplifier, as illustrated, and serves toamplify the detected signaling currents. It is also provided with afeed-back connection 14. which is coupled to the input circuit through atransformer 15. in the normal operation of the amplifier the transformer15 is short-circuited. but the apparatus is so arranged that whenringing cur rent comes in over the line L the short circuit from thesecondary winding of the transformer 15 is opened and the feed-backconnection 14: becomes operative, so that the amplifier now functions asa source of oscillations of ringing frequency which are transmitted fromthe circuit RL, to the channel TL,,'in

which they modulate the carrier frequencyfor transmission to a-distantstation. The incoming circuit RL, also includes a filter This filter maylikewise be of the general type illustrated in the above mentionedpatents to George A. Campbell, and is preferably so designed as totransmit a range of frequencies extending from zero up to the highestfrequency employed in ordinary telephonic transmission. 7

Since it is generally customary to ring over lines such as L, atrelatively low frequencies, such, for instance, as 16 cycles per second,it is desirable that some apparatus should be provided at the junctionbetween the low frequency line and the carrier systern, to translatethese ringing currents into ringing currents of some higher frequencywhich is more suitable for the modulation of carrier currents. It hasgenerally been found that ringing current having the frequency of 133cycles is adapted for this purpose, although it will be understood thatother frequencies may be used if preferred. In order to produce thetranslation in ringing frequency above referred to, the line L, isprovided with a ringing responsive relay 16, which indirectly controlsrelays 17 and 18; the latter serves to convert the amplifier RA, into agenerator of oscillations having a frequency of 133 cycles. The relay 17connects a short circuit across the line L, at the point where it isconnected to the transformer 11, so that the transformer arrangement isunbalanced and the oscillations generated by the amplifier RA, may betransmitted over the circuit EL, to the outgoing channel TL,, where theymodulate the carrier oscillations andare then transmitted to the distantstation.

A ringing responsive relay 19 is bridged across the channel RL,, asindicated, and this relay is adapted to respond to detected 133 cycleringing current and control the action of relays 20 and 21. The relay 20is arranged to apply 16 cycle ringing current to the line L,, the relay21 at the same time connecting an artificial line N, in place of theline L,, so as to prevent singing in the channels BL, and TL,. Thecircuit of the relay 19 is so arranged that when the relay 16 isoperated in response to ringing current the relay 19 cannot be operated.The circuits of the relays 20 and 21 which are controlled by the relay19 arealso arranged to prevent the operation of these relays when therelay 16 is operated. This prevents the possibility of a ring-back or afalse opera- .tion of the relay 20, when the relay 16 responds toringing current incoming from the line L,. I

Tn order to prevent the relay 16 from being operated when 133 cycleringing current is impressed upon the relay 19, a filter comprisingshunt inductance 22 and series ca pacity 23 and 24eis provided in thecircuit RL,, beyond the connection of the relay 19. This filter servesto prevent the transmission of 133. cycle ringing current over thecircuit lRL,, beyond the relay 19, so that the relay 16 will not respondthereto. The circuit of the relay 16 is furthermore tuned to respond to16 cycle current, thereby further prevent-- ing the possibility of afalse operation of this relay, in response to a ringing signal 1received from the line ll TL. Since the pres ence of the filter 22, 23,24 in the circuit RL, would prevent the transmission of 133 piyc-leringing current from the amplifier 1A,- to the circuit TL, in responseto the action of relay 16, relay 17, which is controlled by the relay16, is so arranged as to incense understood from a detailed descriptionof the operation. Talking currents incoming from the line L, aretransmitted through the transformer 11 to the circuit TL, and areimpressed upon the modulator High frequency carrier currents from thecircuit 12 are now' modulated by the modulator M in accordance with thetalking currents and the modulated high frequency currents aretransmitted throu h the filter TF amplified by the amplifier A and thentransmitted through the filter TF to the common circuit TL. Thesemodulated carrier frequencies, together with modulated carrierfrequencies from other channels simultaneously impressed upon thecircuitTL, are transmitted through the transformer 10 to the'main line ML.Modulated carrier currents incoming from the line as, having the theproper frequency, are selected b I filter RF from the circuit RL anpressed upon the detector D,. As a result ofthe reaction of the receivedcarrier currents and the unmodulated carrier currents from the circuit13 in the detector D,, the low frequency talking currents appear in theoutput circuit of said detector, and are impressed-upon the amplifier HAAfter being amplified the, low frequency currents are transmittedthrough the filter RF, to the main line L,.- The filter-22, 23, 24 andthe bridged connection through the relay 19, beirilig tuned to 133cycles frequency, are not e co tive to substantially reduce thetransmission of talking currents, over the circuit Sixteen cycle ringingcurrent incoming from the line L actuates the relay 16, which opens thenormally closed circuit of the relay 25. The latter relay releases its.armature, thereby connecting ground to the circuits ofrela 17 and 18,both of which are energized; elay 18, at its vextreme right hand frontcontact, short circuits the poten-' tiometer in the in ut circuit of theamplifier RA, and at its Inner right hand contact I opens a shortcircuit about the secondary winding of transformer 15, so that the feed-I back 14 of the amplifier RA becomes efiective and the amplifier RA,now functions as a generator of 133 cycle currents, which aretransmitted through the filter RF]. At its outer left hand contact relay18 removes a short circuit from about the resistance 27, which is nowincluded in the circuit RL At its inner left hand contact relay 18 holdsopen the circuits of relays 20 and 21,.to prevent any possibility of thefalse action of these relays, due to the response of the relay 19 to 133cycle current, which might occur owing to, some defect in the circuit.Relay 17 at its lower contact opens the circuit of rela 19 andshort-circuits the condenser 23, so t at 133 cycle current from theamplifier RA may be freely transmitted over the circuit RL,. Relay 17,at its upper front contact, connects a short circuit across the line Lthereby unbalancing the transformer 11, so that 133 cycle current istransmitted through said transformer to the outgoing circuit TL,. Themodulator M now modulates the carrier frequency in accordance with 133cycle current, and the modulated carrier currents are then through thefilter TF amplifier TA filter TF etc. to the main line ML.

Incoming carrier current modulated in accordance with 133 cycle ringingcurrent is transmitted from the main line ML into the circuit RL and isselected through the filter RF and impressed upon the detector D,. As aresult of the action of thedetector, 133 c cle current appears in theoutput circuit t ereof and is impressed upon the amplifier 1 RA Afteramplification by the amplifier RA the 133 cycle current is transmittedthrough the low frequency filter RF, and

flows through the circuit of relay 19-, being substantially preventedfrom passing beyond the junction point of this relay with the circuit RLby means of the filter 22, 23, 24. Relay 19, in response to 133 cycleringing current, opens the circuit of relay 26, so that a circuit iscompleted from ground over the inner left hand back contact of relay 18,back contact of relay 26 and through the windings of relays 20 and 21 tobattery.

Relay 20 disconnects the line L from the transmitted transformer 11 andapplies 16 cycle ringing current over its front contacts to said line.Relay 21, at the same time, connects the artificial line or network N,to. the transformer 11, to maintain the balance of the circuit, Whilethe line L, is disconnected.

It will be obvious thatthe general prin-- ciples herein disclosed may beembodied in many other organizations widely different from thoseillustrated, without departin from the spirit of the invention as definein the following claims:

What is claimed is:

-1. In a multiplex carrier system, a, low frequency signaling circuit, acircuit for the transmission of alternating carrier currents, outgoingand incoming carrier channels for interconnecting saidcircuits, saidchannels 1 including means for translating signaling currents intocarrier currents, and vice versa,

a relay responsive to ringing current -incoming from the signalingcircuit for'applying signaling currents to theoutgoing cari with saidsigna mg circuit for aplying ringing current to said signaling circuit,and means whereby when one of said relays is operated the other relay isprevented from operation. a

2. In a multiplex carrier system, a signaling circuit, a circuit for thetransmission of alternating carrier currents, outgoing and incomingcarrier channels interconnecting said circuits, said channels includingmeans for translating signaling current-s into carrier currents, andVice versa, a relay responsive to ringing current incomin from saidsignaling circuit, means control ed by said relay for applying ringingcurrents to the outgoing carrier channel associated therewith, a relayresponsive to ringing currents transmitted from said carriertransmission circuit to the incoming carrier channel associated withsaid signaling circuit, means controlled by said relay for applyingringing currents to said signaling circuit, and means whereby when oneof said relays is operated the means to apply ringing current con cationof ringing current to said signaling circuit, and means whereby when oneof said relays is operated the operation of the other relay isprevented.

l. In a multiplex carrier system, a signaling circuit, a circuit for thetransmission of alternating carrier currents, outgoing and incomingcarrier channels for interconnecting said circuits, said channelsincluding means for translating signaling currents into carriercurrents, and vice versa, a relay associated with said signalingcircuit, means controlled by said relay for applying ringing current tothe outgoing carrier channel associated therewith, a relay associatedwith the incoming carrier channel interconnecting said signaling circuitand carrier transmission circuit, means controlled by said relay forapplying ringing current to said signaling circuit, and means wherebywhen one oi": said relays is operated the application of ringing currentunder the control of the other relay is prevented- 5. In a multiplexcarrier system, a signaling circuit, a circuit for the transmission ofalternating carrier currents, outgoing and incoming carrier channels forinterconnect ing said circuits, said channels including means fortranslating signaling currents into carrier currents, and vice versa, aringing responsive relay associated with said signaling circuit, asecond relay controlled by said ringing responsive relay for applyingringing current to the outgoing carrier channel associated with saidsignaling circuit, a ringing responsive relay associated with theincoming carrier channel interconnecting said signaling circuit andcarrier transmismission circuit, a fourth relay controlled thereby forapplying ringing current to the signaling circuit, and interlockingconnections between said second and fourth relays whereby when one isactuated the operation of the other is prevented.

6. In a multiplex carrier system, a signaling circuit, a circuit for thetransmission of alternating carrier currents, outgoing and incomingcarrier channels for interconnecting said circuits said channelincluding means for translating signaling currents into carriercurrents, and vice versa, a ringing responsive relay associated withsaid signaling circuit, a second relay controlled by said ringingresponsive relay for applying ringing current to the outgoing channelassociated with said signaling circuit, a ringing responsive relayassociated with the incomin carrier channel interconnecting said signaing circuit and said carrier transrmssion circuit, a fourth relaycontrolled thereby, means whereby when said first-mentioned ringingrelay is operated the operation of said second-mentioned ringing relayis prevented, and interlocking connections between said second andfourth relays whereby when one of said relays is actuated the operationof the other is prevented. I

7. In a multiplex carrier system, a signaling circuit, a circuit for thetransmission of alternating carrier currents, outgoing and incomingcarrier channels for interconnecting said circuits, said channelsincluding means for translating signaling currents into carriercurrents, and v1ce versa, a ringing responsive relay associated withsaid signaling circuit for controlling the application of ringingcurrent to the outgoing channel associated therewith, a ringingresponsive relay associated with the incoming carrier channelinterconnecting said signaling circuit and carrier transmission circuit,and means whereby when said first-mentioned ringing responsive relay isoperated said second-mentioned ringing responsive relay is renderedinoperative.

8. ln a multiplex carrier system, a signaling circuit, a circuit for thetransmission of alternating carrier currents, outgoing and incomingcarrier channels for interconnecting said circuits, said channelsincluding means tortranslating signaling currents into too liill carriercurrents, and vice versa, one of said channels including an amplifier, arelay responsive to rmgmg current mcommg from said signaling line, meansunder the control of said relay whereby said amplifier is caused tosupply ringing current to the carrier transmission circuit, a relayresponsive to ringing current outgoing from the carrier transmissioncircuit said relay controlling the application of ringing current to thesig- 10 naling circuit, and means whereby one of said relavs is renderedineffective when the other relay is operated. I

In testimony whereof, I have si name to this specification this 23rSeptember, 1919.

ed my day of 15 J OHN DAVIDSON, J R. a

